The present invention relates to a head for a printing apparatus such as an ink jet printer in which a plurality of head units are arranged longitudinal, each head unit having pressure producing means in part of a region occupied by a pressure producing chamber that communicates with a nozzle opening, and producing an ink droplet by applying pressure to ink in the pressure producing chamber. More specifically, the present invention relates to a wiring structure for supplying drive signals to the respective head units.
In order to meet the needs for high-speed printing and high-density printing, the number of nozzle openings per recording head is increased. Handling a fluid such as ink, the ink jet recording head is sensitively affected by inconsistency in the fluid resistance or the like of passages such as nozzle openings and pressure producing chambers, and therefore requires uniformity and high accuracy in forming a great number of nozzle openings and pressure producing chambers. In addition, if inconvenience occurs in even only one of members such as a passage or a pressure producing means, print quality is impaired to a great degree, which in turn makes the recording head no use and hence imposes the problem of an extremely low production yield.
In order to overcome this problem, a plurality of recording head units, each having a relatively small number of pressure producing means, are assembled into a recording head in a row. According to this recording head, production yield is improved in compensation for the small number of pressure producing means. As a result, a recording head having a great number of nozzle openings with high production yield can be fabricated.
On the other hand, a drive signal that jets an ink droplet out of a nozzle opening by applying pressure to the ink in a pressure producing chamber of a recording head is supplied through a flexible cable from an external drive circuit. This design requires that at least signal lines equivalent to the number of nozzle openings be provided on the flexible cable. If the number of nozzle openings is increased, a tradeoff between narrow width design for a single signal line and wide width design for a flexible cable must be considered in order to prevent signal attenuation caused by transmission passage resistance.
From the former design arises a problem that a signal attenuate and a time delay in applying pressure to the ink in the pressure producing chamber occurs due to an increase in the resistance and capacitance of the signal line. Further, from the latter design arises a problem that connection between the flexible cable and the recording head becomes difficult because of a large difference in size between the flexible cable and the recording head.
Developed to overcome such problems is a technique, in which a drive signal generating semiconductor integrated device is arranged on the flexible cable. That is, drive signals for applying pressure to the ink in the respective pressure producing chambers is not sent from the external drive circuit, and the print data is fed and the drive signal generating semiconductor integrated device on the flexible cable generates the drive signals. This technique is advantageous in that the drive signals for applying pressure to the ink in the respective pressure producing chambers can be supplied with an extremely small number of signal lines compared with the number of nozzle openings.
Such drive signal generating semiconductor integrated device is arranged on the flexible cable in the following manner. A window, which is a through hole slightly larger than the outer periphery of the semiconductor integrated device, is formed in the flexible cable; tabs are formed by exposing a copper foil inside the window, the copper foil forming a conductive pattern of the flexible cable; and the tabs are soldered to the terminals.
This technique would be very advantageous if drive signals for applying pressure to the ink in all the pressure producing chambers could be generated by a single semiconductor integrated device. However, the number of terminals arranged on the semiconductor integrated device must be equal to that of nozzle openings in order to supply signals to the pressure applying means of the respective pressure producing chambers. Therefore, if the number of nozzle openings amounts to as many as hundreds, the size of a case for containing the semiconductor integrated device must be increased in order to accommodate such number of terminals, which in turn imposes a problem that the semiconductor integrated device becomes unreasonably large in structure. In addition to this problem, there exist not only a problem that the patterns for supplying signals to the respective pressure applying means become too dense but also a problem that the width of the flexible cable must be increased in order to accommodate these patterns.
Thus, an appropriate solution is to divide the nozzle openings into a plurality of groups and allocate a single semiconductor integrated device to each group. However, in this case, conductive path patterns that at least supply power to transmit a print signal to the semiconductor devices from one side to the other side of the flexible cable and to drive these integrated devices are necessary. Therefore, these patterns must be formed so as to make a detour around the windows that allow the integrated devices to be attached to the flexible cable. This requires a reduced width of a wiring pattern, which in turn imposes the problem of impaired reliability, etc.
In order to overcome this problem, it is conceivable to divide the nozzle openings into a plurality of groups and supply a signal every group with a flexible cable dedicated to each group. This, in turn, imposes the problem of difficult cabling, etc.
The present invention has been made in view of the aforementioned circumstances. The object of the present invention is therefore to provide an ink jet recording head capable of supplying drive signals to a plurality of head units by a single flexible cable without decreasing the width of a conductive pattern and increasing the width of a flexible cable.
In order to achieve the above and other objects, the present invention is applied to an ink jet recording head that includes a plurality of recording head units and a flexible cable. Each of the plurality of recording head units has a pressure producing chamber communicating with a nozzle opening, a pressure producing means for applying pressure to the pressure producing chamber, and a connecting terminal for supplying a drive signal to the pressure producing means. The plurality of recording head units are arranged linearly. The flexible cable has a drive signal generating semiconductor device that generates a drive signal for driving the pressure producing means based on a print signal from an external source, supplies the print signal from an external drive circuit to the drive signal generating semiconductor device, and supplies the drive signal generated by the drive signal generating semiconductor device to the pressure producing means while connected to the connecting terminal. In such ink jet recording head, the flexible cable has a widow and a conductive path, the window allowing the drive signal generating semiconductor device to be attached thereto, and the conductive path being formed so as to extend substantially in parallel in a direction of arrangement of the recording head units and being exposed at a window region in such a manner that a metal foil forming the conductive path traverses the window and suspends on the lower surface of the semiconductor device.